The present invention relates generally to a rolling element bearing and cage assembly. More specifically, the present invention relates to a high speed rolling element bearing and cage assembly wherein the cage is designed to reduce or eliminate cavitation of the lubricating oil.
Cavitation damage in the rolling element bearing cage occurs because of back and forth oscillation of the rolling element bearing against the cage within the cage pocket. The frequency, and thus the speed, of this oscillation may be high in high speed rolling element bearings. When the rolling element and cage come closer in proximity, lubricating oil can be squeezed out and, due to the oil's inertia, is unable to move quickly to fill the gap as the rolling element and cage move apart from each other. This creates a low pressure region which results in cavitation where the air dissolved in the oil escapes and forms a bubble. When this bubble collapses, it causes a large, sudden force on the cage resulting in damage at the rolling element/cage interface. This damage causes the cage material to spall and break away from the cage. After repeated cavitation formation and collapse, the cage fails under fatigue.
There have been changes in the design of rolling element bearing and cage assemblies to improve the lubrication of the bearing and cage. However, none of these bearing and cage assembly designs address the problem of cavitation. For example, U.S. Pat. No. 3,597,031 discloses a bearing cage having lubrication reservoirs for lubricating the pocket of the bearing cage. The cage also is provided with lubrication passages for passing the lubricant from the reservoir to the pocket. The passages however, while preventing wear of the cage pilots adjacent to the pocket, do not prevent cavitation wear of the bearing cage assembly.
U.S. Pat. No. 5,584,583 describes a roller and cage assembly having a cage with high rigidity where side slits located between the cage and the weights of a crankshaft provide lubrication to the cage. However, the slits, while being of sufficient width to provide good lubrication to the cage, are too wide to control cavitation.
U.S. Pat. No. 6,533,462 provides a cage assembly for rolling element bearings having grooves to provide grease lubrication to the bearing. The grooves are internal and circumferential to the cage pocket and connected to a grease lubricant storing cavity. The cage assembly is designed for lubrication of slower speed ball bearings, and therefore uses lubricating grease rather than oil. The cage assembly, while providing sufficient lubrication to the cage pocket, does not prevent cavitation of lubricating oil.
As can be seen, there is a need for rolling element cage assembly that eliminates cavitation of lubricating oil. Methods for use of such a rolling element cage assembly in high-speed applications would also be desired. Elimination of the cavitation will increase the life of the rolling element cage by decreasing wear and subsequent fatigue failure of the cage.